In standard belt tensioners presently used in motor vehicles, the retraction device is operated by a spiral spring, which has a design-based initial tension when the belt is extracted, and is increasingly tensioned according to its spring characteristic as the belt is pulled out.
The extraction lock operates with mechanical catch members. On one hand, these are controlled by inertial members, which are displaced from an inactive catch-bolt position to an active catch-bolt position, when forces acting on the vehicle body produce a body acceleration or deceleration that exceeds a low threshold value. On the other hand, centrifugal-force members are displaced from an inactive catch-bolt position to an active catch-bolt position, when a reel used for receiving the belt is rotated in the extraction direction of the belt, at an angular acceleration exceeding a threshold value or in a jerky manner. This ensures that the belt is restrained from being pulled out (further) in driving situations tending to be dangerous, or even in crashes.
In view of the fact that drivers and/or, in particular, passengers of a vehicle may assume a position outside of the normal or desired sitting position, the seat-belt tensioners, at least those in higher-quality vehicles, are assigned irreversible tensioning devices, which typically function and are triggered in a pyrotechnic manner, when a corresponding sensory system “reports” a collision of the vehicle or activates an airbag present in the vehicle. These irreversible belt tensioners are used to shorten the seat belt, using a large force. In this manner, any belt slack at the body of the occupant, as well as at or on the reel of the belt, is eliminated, and the optimum safety of the specific occupants from possible secondary collisions is even ensured after a previously activated airbag relaxes. In any case, the occupant is kept away from hard structural members of the vehicle body as much as possible.
The irreversible tensioning device may be positioned at a limit stop of the belt, on the seat-belt buckle, or on the belt retractor.
To improve comfort, German Published Patent Application No. 39 38 081 describes assigning an electric motor to the spring provided for actuating the retracting device, in order to adjust or move the relatively stationary retainer of the return spring. In this manner, the belt tension may be changed, and in particular, the tension of the belt may remain low and the wear comfort may be improved accordingly, even when the belt is pulled out very far, as is necessary in the case of above-average height or corpulence of the occupant. As soon as the belt is retracted for rolling it up, the relatively stationary retainer is returned by the abovementioned motor to a starting position, so that the belt may be rolled up safely.
Similar arrangements are the subject matter of German Published Patent Application No. 41 12 620 and German Published Patent Application No. 195 01 076.
German Published Patent Application No. 100 13 870 describes that one can reversibly increase the belt tension, when a sensory system signals a dangerous driving condition. This prepares the belt for a crash of the vehicle.
It is an object of the present invention to improve the tightening of the belt with regard to aspects of both safety and comfort.